1. Field of the Invention
The present invention relates to the improvement of an image filing apparatus such as an optical disk, or an electronic filing apparatus, and more particularly to an image filing apparatus providing image data suitable for output types of several input/output devices.
2. Description of the Related Art
Generally, a scanner, a printer and a CRT are used mainly as input/output devices in such an image filing apparatus.
There are many types of methods of displaying a tone image in use for these input/output devices. For example, the binary method and the multi value method are applied widely for the scanner. In the printer, the binary method is used mainly, especially for the laser printer, the binary method and the area tone method are applied widely. In addition, there are many methods such as the binary method, the multi value method and the color method for the CRT. Thus, many types of methods of displaying a tone image are available for input/output devices.
Conventionally, image data processed by such a method (the binary method, the multi value method or the color method) are compressed and extended using a standard data compression and extension method. For example, the method (MH, MR, or MMR) using the Huffman coding is well known for the compressing and extending process of binary image data. Recently, a method referred to as arithmetic coding has been used widely. In the compressing and extending process multi-valued image data or color image data, generally, two-dimensional orthogonal transforming method called as Adaptive Discrete Cosine Transform (ADCT) is used widely. Thus, there are several data compression and extension methods according to types of input/output devices.
Usually, an image forming apparatus is provided with a plurality of input/output devices, For example, a printer, a scanner, a CRT and the like. As mentioned above, the binary method is most widely used for a printer. Therefore, a transformation from a multi value to a binary value is performed on data input through the scanner in an image processing unit of the apparatus. Further, the display using binary data must be used for the CRT in accordance with the outputting type of the printer. The result is that there is a decrease of the CRT's power of expression caused by the decrease of the amount of information.